JPH0119231B2 - - Google Patents

Description

Detailed Description of the Invention The present invention uses alkali metals such as lithium and sodium, alkaline earth metals such as magnesium and calcium, or light metals such as aluminum as negative electrode active materials, and uses metal fluorides, chlorides, oxides, or carbon atoms as negative electrode active materials. Lithium perchlorate is used as a positive electrode active material, and lithium perchlorate,
This invention relates to improvements in the positive electrode of so-called organic electrolyte batteries that use organic electrolytes in which solutes such as lithium borofluoride and aluminum chloride are dissolved.

Currently, solid active materials commonly used as positive electrode active materials for organic electrolyte batteries include carbon fluoride, manganese dioxide, copper oxide, trilead tetroxide, ferrous sulfide, ferric sulfide, and sulfite. gas,
Examples include gaseous or liquid active materials such as thionyl chloride. All of these active materials have extremely low conductivity, and in the case of solid active materials in particular, in order to use them as positive electrodes for batteries, it is necessary to add carbon powder or metal powder as a conductive material. Therefore, selection of an appropriate binder is an important requirement in order to form a positive electrode molded article from these mixtures.

Furthermore, since an organic solvent is used as the electrolyte, a binder that is resistant to organic solvents must be used, and it can be said that the degree of freedom in selecting a binder is further limited by this.

Conventionally, in organic electrolyte batteries, fluororesins such as tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene have been used mainly because they are stable in organic solvents. powder or dispersed in water using a surfactant, styrene-butadiene rubber (SBR resin) dissolved in an organic solvent, or dispersed in water using a surfactant, etc. It's here.

From the viewpoint of handling, it is easy to use these as powders, but in that case they must be uniformly dispersed and
In order to provide binding properties, it is necessary to mix approximately 20% by weight of the total. Therefore, if approximately 10% by weight of the conductive material is mixed, the pure active material in the positive electrode mixture will inevitably be as low as approximately 70% by weight, and the ratio of the binder covering the surface of the active material will also be large, which will affect the characteristics. itself is greatly reduced.

On the other hand, when using a binder dispersed in water using a surfactant, the amount of binder is small at 15 to 5% by weight of the total, although it is somewhat inconvenient to handle, and the energy density is is very advantageous.
In particular, when a styrene-butadiene rubber dispersion is used, when 10% by weight of carbon powder is added to the conductive material, the amount required is as small as about 5% by weight, making it the most advantageous among these binders.

On the other hand, since all of these resins have oil repellency, they do not mix well with the electrodes, and the penetration of the electrolyte into the interior of the electrodes is extremely hindered. This oil repellency is smaller for styrene-butadiene rubber than for fluororesin,
In this respect as well, it can be said that it is advantageous since it can be minimized in terms of quantity.

However, in order to provide binding properties with a small amount, it is necessary to mold the electrode under high pressure, and styrene-butadiene rubber itself has some degree of oil repellency, so the electrolyte does not enter the inside of the electrode. Penetration is difficult, which adversely affects the discharge characteristics of the battery. That is, there is a delay in the voltage at the start of discharge, an effect on the discharge utilization rate, etc.

Therefore, in order to eliminate these drawbacks, it is necessary to further reduce the amount of binder and to increase the porosity of the electrode to facilitate penetration of the electrolyte.

As a result of various studies in view of the above, the present inventors found that
Polyvinylpyrrolidone It has been found that the above-mentioned drawbacks can be improved by adding the above to the positive electrode mixture.

Polyvinylpyrrolidone is soluble in organic solvents, especially propylene carbonate, γ-butyrolactone,
When it is added to an electrode mixture, formed into a molded body, and then incorporated into a battery, it gradually dissolves into the electrolyte. Therefore, it is thought that the portion of the electrode where polyvinylpyrrolidone was present is replaced with the electrolyte, increasing the reactive portion of the electrode. As a result, the discharge characteristics of the battery are improved and the discharge utilization rate of the electrode mixture is improved. At the same time, since polyvinylpyrrolidone itself has binding properties, it also has the effect of reducing the amount of binding agent.

Normally, once the electrodes of a battery are incorporated into the battery, they can be fully utilized even if their strength is somewhat weak. Therefore, when a smaller amount of binder than usual and a predetermined amount of polyvinylpyrrolidone are molded together with a positive electrode active material and a conductive material, a strong electrode can be obtained due to the binding properties of polyvinylpyrrolidone, which can be used in the battery assembly process. It does not crumble when handled, and can be handled in exactly the same way as a normal electrode. Moreover, since only the polyvinylpyrrolidone dissolves into the electrolyte after being incorporated into the battery, the strength of the electrode itself is slightly reduced. However, it cannot affect the battery performance at all. Moreover, since the absolute value of the binder amount is small, the electrolyte and electrode become more compatible, and the dissolution of polyvinylpyrrolidone increases the porosity of the electrode, resulting in a dual effect such as improving the discharge characteristics of the battery. It will be done.

Hereinafter, the present invention will be explained with reference to examples thereof.

Example 1 Carbon fluoride powder, acetylene black as a conductive material, and polyvinylpyrrolidone in a weight ratio of 100:11:
Further, 100 g of this mixture and 5 g of an aqueous dispersion of styrene-butadiene rubber (resin content 50% by weight) were thoroughly mixed, and after the water was evaporated, 1 g of the mixture was mixed into a 20 x 20 mm A titanium net current collector is sandwiched between the two and pressure molded at a pressure of 1 ton/cm ² to obtain a positive electrode.

The negative electrode was constructed by pressing 0.2 g of a metal lithium sheet onto a 20 x 20 mm nickel net current collector. The two negative electrodes are stacked on both sides of the positive electrode wrapped with a separator made of a nonwoven polypropylene fabric, and sealed together with an electrolyte in a polyethylene container to prepare a test battery. The electrolytic solution used was one in which lithium borofluoride was dissolved in a mixture of equal volume of propylene carbonate and 1,2-dimethoxyethane at a ratio of 1 mol/mole. This battery is called A.

Next, to 100 g of a mixture of fluorocarbon and acetylene black at a weight ratio of 100:11, 50 c.c. of water in which 0.7 g of polyvinylpyrrolidone was dissolved and an aqueous dispersion of styrene-butadiene rubber (resin content 50 Add a mixture of 5 g (% by weight) and mix thoroughly to evaporate water. A battery is constructed by taking 1 g of this and molding it into a positive electrode in the same manner as described above. Let this be B.

In addition, as a comparative example, 10g of a mixture of fluorocarbon and acetylene black at a weight ratio of 100:11 was mixed with 10g of an aqueous dispersion of styrene-butadiene rubber (resin content 50% by weight), and water After volatilizing it, 1 g of it is taken and molded into a positive electrode in the same manner as above to construct a battery. This is C
shall be.

Although the weight of the positive electrode is the same in both batteries, the theoretical filling amount is 760 mAh for A and B, and 740 mAh for C. The filling amount of negative electrode lithium is 1.5Ah.
This was taken into consideration so that the characteristics of the positive electrode could be compared.

Immediately after prototyping each of the above batteries, 16mA at 20℃
Figure 1 shows the characteristics when discharging at a current of 60
Figure 2 shows the characteristics when discharged under the same conditions after storage at ℃ for one month.

As is clear from FIG. 1, the theoretical filling amount of batteries A and B is only about 3% larger than that of battery C, but the actual discharge amount is about 10% larger. In addition, the voltage at the start of discharge and the flat voltage are also slightly higher. This is thought to be due to the fact that the amount of binder is small and the electrolyte is well adapted to the electrode, and the polyvinylpyrrolidone is dissolved, increasing the porosity of the electrode and increasing the reaction area.

This tendency is more apparent in FIG. In other words, after storage at a high temperature of 60°C, battery C
While the characteristics of batteries A and B slightly deteriorated,
In this case, the effect of polyvinylpyrrolidone is more pronounced, and in fact, it shows better properties than immediately after trial production.

As can be seen from these results, it can be said that the effect of adding polyvinylpyrrolidone is extremely large.

Example 2 Next, 100 g of a mixture of manganese dioxide powder and acetylene black as a conductive material at a weight ratio of 100:5 was mixed with 50 c.c. of water in which 0.4 g of polyvinylpyrrolidone was dissolved and an aqueous solution of styrene-butadiene rubber. A mixture of 3.5 g of dispersion (resin content 50% by weight) is added, kneaded, and then the water is evaporated.
2 g of this was taken, and a titanium net current collector with a size of 20 x 20 mm was sandwiched between them and pressure molded to obtain a positive electrode. A test battery is prepared in the same manner as in Example 1 using this positive electrode. This battery is designated as D.

In this example, the electrolytic solution used was one in which lithium perchlorate was dissolved in an equal volume mixture of propylene carbonate and 1,2-dimethoxyethane at a ratio of 1 mole/mole.

In addition, as a comparative example, 7 g of an aqueous dispersion of styrene-butadiene rubber (resin content 50% by weight) was mixed with 100 g of a mixture of manganese dioxide and acetate black at a weight ratio of 100:5, and after the water was evaporated, the mixture was 2 g was taken and a positive electrode was made in the same manner as above to construct a battery. This battery is called E.

The theoretical charging capacity of the positive electrode of battery D is 574 mAh, and that of battery E is 567 mAh.

16mA at 20℃ immediately after prototype production of these batteries.
Figure 3 shows the characteristics when discharging at a current of 60
Figure 4 shows the characteristics when discharged under the same conditions after storage at 1 month at ℃.

In this example, as in Example 1, the effect of adding polyvinylpyrrolidone is remarkable.

As in the above example, the effect is the same whether polyvinylpyrrolidone is added to the positive electrode mixture as a powder or as an aqueous solution. When the positive electrode active material is a metal oxide such as manganese dioxide and has a large difference in specific gravity compared to polyvinylpyrrolidone, it is advantageous to use an aqueous solution that can be mixed uniformly.

The present invention is applicable not only to the above-mentioned carbon fluoride and manganese dioxide, but also to cases where copper oxide, trilead tetroxide, iron sulfide, etc. are used as the positive electrode active material.

As described above, according to the present invention, a positive electrode with excellent discharge characteristics and storage characteristics can be obtained.

[Brief explanation of drawings]

Figure 1 shows the discharge characteristics of fluorocarbon-lithium batteries immediately after prototype production using positive electrodes manufactured by various manufacturing methods, Figure 2 shows the characteristics after storage, and Figure 3 shows the characteristics of carbon-lithium fluoride batteries using positive electrodes manufactured by various manufacturing methods. Figure 4 shows the discharge characteristics of the manganese dioxide-lithium battery immediately after trial production, and the characteristics after storage.

Claims (1)

[Scope of Claims] 1. A method for producing a positive electrode for an organic electrolyte battery, which comprises molding a positive electrode mixture to which a binder and polyvinylpyrrolidone are added. 2. The method for producing a positive electrode for an organic electrolyte battery according to claim 1, wherein a binder is added after adding polyvinylpyrrolidone powder to the positive electrode mixture. 3. The method for producing a positive electrode for an organic electrolyte battery according to claim 1, wherein polyvinylpyrrolidone is added to the positive electrode mixture as an aqueous solution.